Tuned mass dampers are a well known solution to reducing the amplitude of unnecessary or harmful mechanical harmonic vibrations. Tuned mass dampers are used to dampen vibrations of a large scale from microcircuits to tall sky scrapers. The basic idea behind a tuned mass damper is simple: an auxiliary mass is attached to the vibrating structure via a suspension element, which typically consists of a spring and a damper, thus changing the vibrating characteristics of the vibrating structure. Instead of a spring and a damper, the suspension element may be alternatively provided by means of only one element, e.g. a rubber spring which contains both needed properties.
The mass damper is tuned to the vibrating structure such that the mass of the auxiliary mass and the stiffness of the suspension element are selected to provide an appropriate counterforce to the disturbing excitation force. In particular, the mass ratio, i.e. the relativity of mass between the auxiliary mass and the vibrating structure, and the tuning frequency of the mass damper are calculated according to well known design principles.
While tuned mass dampers are typically linear, also non-linear mass dampers have been proposed by several publications because non-linear mass dampers work on a wider frequency band. Non-linear tuned mass dampers employ a non-linear spring and/or a non-linear damper and mass. One particular type of non-linear mass dampers is a wire rope spring damper, the principles of which have been disclosed in e.g. ‘Parametric experimental study of wire rope spring tuned mass dampers’ Gerges & Vickery in the Journal of Wind Engineering and Industrial Aerodynamics (91, 2003, 1363-1385). According to Gerges & Vickery, the studied frequency area of the resulting structure is at most 4.5 Hz.
An issue associated with conventional tuned mass dampers is that they are and can only be tuned to a rather narrow frequency band. The operational window of a conventional tuned mass damper is dictated by the dampening construction in that the width of the frequency band is a trade-off between high dampening efficiency and width of the frequency band. More particularly, an increase in dampening efficiency typically leads to reduced frequency band, whereas widening the frequency band tends to make the dampening less optimal for a specific frequency within the band. There have been many attempts to broaden the frequency band of mass dampers. Many proposals involve the use of active or adaptive mass dampers which employ a controlling unit regulating a series of actuators which adapt the mass damper to dampen a desired frequency. Otherwise, such active mass dampers are designed similarly to passive dampers in terms of providing a counter mass via a suspension to the vibrating structure. Unfortunately, conventional active mass dampers use excessive energy and are rather complex and therefore not feasible to dampen small and inexpensive structures such as microcircuit boards.
It is therefore an aim of the present invention to provide a simple tuned mass damper which has a broadened frequency band and which can be adapted to large and expensive structures as well as small and inexpensive structures alike.